Monthly Archives: November 2010

The problems appear in etching process

Do you know what problems will appear in etching process of flexible circuits? Ok, follow me to know the details:

1) Etching speed is geeting slower
This is usually because of the low temperature, low spray pressure or chemical proportion of etching solution. But if  these conditions under well control, the etching speed slow may be due to the dissolution copper content is too high. At this point, it is necessary to adjust the etching solution.
2) Precipitation appear in solution
This is due to lack of complexing agent Cl-, or the dilution caused by water. Precipitate is Cu2Cl2: insoluble in water.
3) Resist layer is damaged:
When excess acid is being, this phenomenon appeared. Especially in higher temperatures will appear. Now we can replaced by NaOH or water to adjust. If the acid concentration and the conditions are suitable, then the problem may be due to  improper cleaning of the board or exposure of flexible pcb.
4) The yellow residue in the copper surface
This residue is generally copper hydroxide, which does not dissolve in water. When the board is etched or alkaline cleaning to as the residue left on the board. In addition, when Cl-concentration and the acidity is too low in etching solution, after etched the white precipitate appeared on board, which may be insoluble Cu2Cl2 precipitation. Now we can use 5% hydrochloric acid solution to wash, and last wash by water.

When we know the above problems will appear in the etching process of flex circuits, so we will make the well quality controlling system to control these problems, and then ensure high quality flexible circuits, flex pcb.

Flexible circuits Developing Quality Check

Let’s tell you one way to check the trace quality is good or not after developing of flexible circuits. After developing, even if some developing trace is dirty, or the base is long, is unable to check them out with a magnifying glass; but Cucl2 test is a non-destructive testing way. Testing methods are as follows:
1) First to clean the flexible pcb surface after developing, for example:
After developing → acid washing → acid etching → acid 
2) in a 5% Cucl2 solution for 30 seconds, the best to swing liquid slightly, and use a sponge to remove small air bubbles on the board to invoid to affect judgments.
3) washed
4) drying
5) visual inspection
The copper surface of normal developing will form a layer of gray and black oxide layer after handling.  When the  surface of flex pcb with dry film glue, there will still maintain a bright copper color. This method can be tested if developing of flexible circuits is good.

Related Posts:
1.Drilling of flexible circuits;
2.FPC Exposed Process Operation Notes.

Solution configuration of FPC developing process

Developing process of flexible circuits is the unexposed active group of photographic film part response to dilute alkali solution to the produce soluble substances and dissolve, leaving the already sensitive graphical circuit pattern. The most common used liquid is made of Na2CO3, weight content ratio between 0.75% and 2%.

Dry or wet film load is small, so the correct solution configuration of flexible pcb is the most basic step, in order to accurately control the concentration, we use acid-base titration method calculate the concentration of Na2CO3.
Reference to below methods:
(1) Sampling 25ml developing liquid in 250ml beaker;
(2) by adding D.I. water 100ml and 3-5 drops of methyl orange;
(3) use 0.1N hydrochloric acid to titrate the color changed to red;
(4) Calculate: wt% Na2CO3 = 0.0212 × titre (ml).

Usually dry film in 1% Na2CO3 developing liquid, the loading is about 12-15 mil-ft2/gal. At a higher developing pressure and under the full water washing can be obtained higher loading.

DI water, soft water is recommended for developing of flexible circuits, the use of hard water would have caused the hard dirt to clog of the nozzles.

FPC Exposed Process Operation Notes

Today follow me to know the FPC exposed process operation notes, exposed is the very important step of making flexible circuits.

(1) The vacuum framework of exposure machine is essential, vacuum degree≥ 90%, only through the vacuum machine to let film tightly with the base substrate, and to ensure that no distortion of the circuits in order to improve accuracy.
(2) After the exposed, should immediately remove the panels, otherwise peripheral vision of light will cause unwanted film in developing of flex circuits.
(3) Working conditions must be met: clean (10,000 scale or higher) operating under yellow light, indoor temperature and humidity (21 ± 1 ℃, 55 ± 5%). Exposed machine should have the cooling air exhaust system.
(4) Exposed, the film emulsion side must face down, and  firmly stick the light-sensitive surface side to improve the resolution for circuits.
(5) Exposed machine should regularly calibrate to ensure accurate exposure.

Related Posts:
1. The structure of FPC;
2. Flexible Circuits Production Process;
3. The stiffener of flexible circuits.